1. Field of the Invention
This invention relates to a semiconductor bonding process, and more particularly to a method for eutectically die bonding gallium-type light emitting diodes to a metallized substrate or interconnection member.
2. Description of the Prior Art
It is necessary to obtain mechanical strength, good heat transfer capability and an extremely low ohmic resistance contact in bonding a light emitting diode to an interconnection substrate, such as, a header or strip in order to optimize device performance and reliability. The extremely low resistance ohmic characteristic is necessary as many light emitting diode packaging schemes employ a single lead or connection between the active device and input/output connections, pads, pins, etc. An electrical path between the light emitting diode chip and a metallized substrate completes the circuit and thus only a single lead is required.
Previously, either epoxy die bonding or preform die bonding was used to attach light emitting diodes to metallized members or substrates such as, headers or strips. The epoxy technique generally requires longer overall processing time in addition to the specific cure time inherent in this technique. Further, the epoxy bond does not provide optimal heat transfer between the light emitting diode semiconductor member and its interconnection substrate. Similarly, the preform technique is more expensive and requires longer processing and assembly time. Also, it is yield limited in that often times electrical shorts are created due to the existence of excess metal associated with this process. That is, the use of a preform metal blank for joining the semiconductor light emitting diode chip or die to the interconnection member impedes close quality control of the amount and containment of the metal system.
Therefore, it is an object of the present invention to provide a faster, more economical method of joining gallium-type light emitting semiconductor diode devices to a metallized substrate, interconnection or frame member.
Another object of the present invention is to provide a method of attaching light emitting diode chips to an interconnection member wherein the thermal conductivity between the bonded final package is higher than previously obtainable without sacrifices in cost or time.
Another object of the present invention is to provide a highly efficient economical method of interconnecting a gallium-type LED, i.e., comprising a highly active metal to an interconnection structure with a eutectic bond which possesses excellent mechanical strength, high heat transfer characteristics and low ohmic resistance.
In accordance with the aforementioned objects, the present invention provides a method for eutectically bonding a gallium-type semiconductor-type light emitting diode to an interconnection member by preparing the backside surface of the semiconductor wafer and then evaporating a first alloy layer; such as gold-germanium or gold-silicon, over the back surface. Thereafter, the deposited layer is alloyed at approximately 370.degree. C in forming gas. Next, a second gold-germanium or gold-silicon layer is evaporatively deposited over the first layer. Then, the wafer is separated into separate dies or chips and individual dies are eutectically bonded to a metallized interconnection member or substrate.